Writing instrument



WRITING INSTRUMENT Filed July 10, 1961 I 31/ IZ4 /26 FIG. ,1

FRANK $365??? 4 m5 ATTORNEYS United States Patent 3,082,740 "WRITINGINSTRUMENT Frank A. Eckerle, Tenafly, Ni, assignor to NorthernIndustrial Products Company, Hachensack, NJ. Filed July 10, 1961, Ser.No. 122,884 4 (Zlaims. (ill. Hit-42.4)

This invention relates to ball point pens of the type provided with arelatively large diameter ink cartridge and, more particularly, to a newand improved ball point pen having a large diameter ink cartridge whichcannot leak.

This application is a continuation-impart of my copending United Statesapplication Serial Number 83 6,107, filed August 26, 1959, for WritingInstrument, now abandoned.

Customarily, ink cartridges for ball point pens carry a ball tip at oneend and are open to the atmosphere at the other end to permit air toenter the cartridge as the ink is dispensed through the ball tip byrotation of the ball during writing. 'If the inner diameter of the inkcartridge is small enough so that it acts as a capillary, ink isnormally retained within the cartridge regardless of its orientation. Inorder to provide a cartridge of reasonable length having a larger inkcapacity, however, the diameter must be increased beyond the maximumvalue at which the cartridge acts as a capillary, and in suchcartridges, a seal must be provided to prevent ink from leaking out ofthe open end of the cartridge.

Conventional seals for larger-than-capillary cartridges are of either oftwo types, each of which has certain disadvantages. One type ofconventional seal, such as that described in the Henriksen Patent No.2,678,634, for example, comprises a non-rigid plug located at the rearof the ink column consisting of a pasty mass of grease, parafiin or wax.This form of plug tends to mingle with the ink in the reservoir untileventually it becomes ineffective to prevent leakage. Moreover, the plugmaterial is apt to contaminate the ink. The other type of conventionalseal utilizes a rigid piston follower, such as the one shown in theCofield, In, et al. Patent No. 2,777,422 for example, which necessarilyrequires that a clearance be provided between the piston and the innercartridge wall in order to permit the piston to move within thecartridge as the ink supply is depleted. This clearance is usuallyfilled with a thin flowable liquid sealing material, such as thethixotropic liquid described in the Cofield, Jr., et al. patent forexample, inasmuch as a certain amount of the sealing material isdeposited on the cartridge wall as the piston moves within thecartridge, a substantial supply of the material must be provided.

Heretofore, the supply of sealing material for a rigid piston followerof this type has been retained in place by inserting it between twoseparated pistons or through a transverse bore in the piston into anannular space or cavity formed in the periphery of the piston, both ofwhich constructions are illustrated in the Cofield, J r., et. al.patent. In the latter case, because a thin, flowable sealing material isused, there is not-hing to prevent it from flowing back through the boreand running out of the piston after it has been inserted. Furthermore,the rigid piston follower arrangements not only require complexfabricating and assembly operations but also, because the supply ofsealing material is relatively free to flow, is unenclosed, and isseparated from the ink by only a short distance along the clearancespace between the piston and the cartridge wall, such pistons frequentlypermit ink to invade and mingle with the supply of sealing material,thereby degrading it. Moreover, when ink does invade the annular spacesurrounding the piston, which is almost inevitable as the piston movesforwardly in the cartridge,

known type.

BhfiSZfl ill Patented Mar. 26, I953 ice 2 the entire supply of sealingmaterial becomes contaminated and theeffectiveness of the seal is soonlost. In addition, pistons of'this type also allow substantialquantities of sealing material to rise through the column of ink'toobstruct the writing point when the penis inverted.

Accordingly, it is an object of the present invention to provide a newand improved ball point pen which effectively overcomes theabove-mentioned disadvantages of the prior art constructions referred toabove.

Another object of the invention is to provide a sealing arrangement fora ballpoint-pen cartridge of greater-thancapillary diameter which is ofsimple construction and continuously r'enews the "seal during use ofthepen.

A further object of the invention is to provide a new and improvedpiston follower'for ink cartridges.

An additional object of the invention is to provide "a single pistonsealing arrangement for ball point pe'n ink cartridges which is simpleto manufacture, is of rugged construction, is inexpensive, and isgenerally superior to prior art sealing arrangements.

These :and other objects of the invention are accomplished by providinga single cup-shaped rigid follower piston having an interior cavitywithin the piston and a plurality of openings inthe wall of the pistonproviding communication between the interior cavity and the outersurfiace thereof. In order to provide a seal within the ink cartridge ofa ball point pen, the internal cavity in the piston is filled with asealing material having the consistency of a paste, as opposed to theprior art free-flowing type of material, and the annular clearance spacebetween the piston and the inner cartridge wall, along with the openingsleading thereto, are also filled with the same sealing material.

In a preferred embodiment, the piston has two spaced shallowcircumferential grooves which are partly cut through to form slots whichcommunicate with the interior cavity. The provision of the grooves andslots results in the formationo f external piston rings of sealant whichpiston rings seal against the ink tube wall. The embodiment assuresuniform distribution of the sealant about the piston exterior, thusproviding a particularly effective seal.

Further objects and advantages of the invention will be apparent from areading of the following description in-conjunction with theaccompanying drawings inwhich: I FIG. 1 is a view in elevation, partlybroken away, illustrating a typical ball point pen ink cartridge havinga single piston seal arranged according to the invention;

FIG. 2 is a perspective front elevation view of the sealing pistonutilized in the cartridge of FIG. 1; and

FIG. 3 is a view in longitudinal section of another piston arrangedaccording to the invention.

Referring now to the drawings, and in particular to FIGS. 1 and 2,reference numeral 10 generally indicates a typical ball point pen inkcartridge having a seal arranged according to the present invention. Thecartridge comprises a tube of the conventional type generally referredto by numeral 2 having a narrow neck portion 3 and a Wider reservoirportion 5. The neck portion 3 carries at its forward end a ball tipportion generally indicated by reference numeral 11. The ball tipportion includes a ball proper 4, rotatably mounted in the tube tip 6 inconventional manner. The tip tube 6 has an enlarged rear portion 8 whichis press fitted into the forward end of the neck portion 3 of thecartridge.

The diameter of the reservoir 5 of the tube 2 is larger than the maximumdiameter capable of acting as a capillary and is filled with ink orsimilar writing fluid 12. Preferably the fluid 12 is the usualrelatively thick and viscous ink customarily used in ball point pens,but of course if desired, the writing fluid may be of any other The inkor writing fluid is dispensed during writing by the rotation of the ball4 as is well known in the art.

The rear end 14 of the tube 2 is open and in order to prevent the inkfrom flowing out through the opening 14 a piston member generallyreferred to by reference numeral 30 is placed on top of the ink. Detailsof the construction of the piston 30 as used in the embodiment of FIG. 1can be seen from FIG. 2. It will be noted that the piston issubstantially cylindrical and cup-shaped, having a hollow interiorforming a storage space 34. The piston 30 is provided with two spacedcircumferential grooves 20 and 22, respectively, of relatively shallowdepth. Groove 20 is cut through along a portion of its circumference soas to form a slot 24 while groove 22 is correspondingly cut throughalong a different portion of its circumference so as to form a slot 26.The slots 24 and 26 thus communicate with the storage space 34. It willbe noted that the slots 24 and 26 occupy more than half of the groovecircumference and that they are partly overlapping. The grooves 20 and22 are thus the extension of slots 24 and 26, respectively. The pistonalso has a tapering lower portion 28 as seen in FIGS. 1 and 2. The outerdiameter of the piston 30 is only slightly smaller than the innerdiameter of the tube 2 so that the piston, with very little play, fitscoaxially into the space defined by the tube 2 to form a gap 40 having awidth of 0.0020.020". In order to keep the piston member 34 in positionat the upper surface of the ink when the pen is in the writing position,the member is formed of a material having a specific gravity slightlyless than that of the ink 12 and which is not soluble in or misciblewith the ink. Typically, the specific gravity of the material used forthe piston 34 is about 1.06, while that of the ink is about 1.14.Inasmuch as the seal effectively prevents any ink from passing to theother side of the piston member, it will be apparent that the pistonremains as a barrier between the ink and the air in the cartridgeregardless of the orientation of the writing instrument. The preferredmaterial for the piston member 34 is an acrylonitrile butadiene styrenecopolymer, such as the material commercially known as Kralastic MM.Other lightweight plastic materials are also suitable for use infabricating the piston member.

A sealing material 32 (FIG. 1) is inserted into the hollow interior orstorage space 34 of the piston. When the cartridge is originallyassembled, the piston 30 is placed on top of the ink column 12whereaf-ter the sealing material 32 is injected into the piston, wherebya small amount of the sealing material will be urged through theopenings or slots 24 and 26.

Inaccordance with the invention, the sealing material 32 has plasticcharacteristics and is thus displaceable under the action of a movingforce in any direction and without rupture, is non'thioxtropic and has apasty consistency. Obviously, if the sealing material were thixotropic,it could not have the desired paste-like consistency under allconditions. Further, the sealant is temperature stable within a range ofapproximately to 200 F. The temperature stability of the sealant isimportant because ball point pen cartridges are subjected to varyingtemperatures within wide ranges. Thus, the ball point pen may be exposedto winter temperature, on the one hand, and to direct sunlight in a showcase or display window, on the other hand, while the user will expectproper functioning under all these conditions. The sealant also shouldhave a worked penetration of approximately 300-385 mm./10 in accordancewith A.S.T.M. test D2l7-52T. Penetration is a measure of the consistencyof a material and is expressed as the distance in tenths of a millimeterthat a standard cone passes vertically into the material at atemperature of 77 F. during a period of seconds. Also the specificgravity of the sealant has to be less than that of the piston and of theink. This is so because the assembled cartridge is normally subjected tocentrifugation to expel trapped air. If the specific gravity of thesealant were greater than that of the ink, the sealant would be urgedtowards the ball tip during the centrifugation. In addition, the sealingmaterial should have a minimum tendency to bleed or form oils or otherliquids which could flow freely into the ink supply and, for thisreason, materials containing highly effective thickening agents arepreferred. Extensive experiments have shown that particularly useful inthis regard is the material known commercially as Rykon No. 0 which is apetroleum grease containing an organic thickening agent. Rykon ismanufactured by Superla Products, Inc., of Chicago, Illinois.

A sealant of the kind defined which is injected into the interior cavity34 of the piston will exit through the discharge openings or slots 24and 26 and into the narrow gap 40 between the ink tube wall and thepiston to fill the latter and to form a thin but effective seal betweenthese two elements, thus preventing ink from reaching the open rear endof the cartridge.

In operation, as ink from the reservoir is drawn through the ball tip byuse of the pen, the buoyant effect of the ink on the piston is reducedand the piston moves toward the forward end of, the cartridge. Inasmuchas the sealant has the properties and characteristics set forth above,it permits the piston to slide forwardly easily in the cartridge whileat the same time maintaining its shape and providing an effective seal.Moreover, as a deposit of sealing material is left behind by the forwardmotion of the piston, a corresponding amount of fresh sealing ma terialis drawn through the slots 24-, 26 from the supply within the cavity 34,thus renewing the sealing material in the gap at a point close to theink supply. This is due to the suction action produced by the rotatingball. In this way, any sealing material which has been contaminated byinvasion of ink from the tube is displaced rearwardly and replaced byuncontaminated material adjacent to the ink supply, the contaminatedmaterial eventually being left behind on the cartridge wall. As aresult, an effective seal is maintained throughout the life of thecartridge.

During this process, the sealing material which emeregs through theslots 24 and 26 will enter the narrow gap 40 formed between the innerface of tube 2 and the outer piston surface to form two sealing pistonrings at the level of the grooves and slots. The formation of the ringsof sealing material is facilitated by the construction of the piston. Asthe grooves 20 and 22 extend circumferentially they will be entirelyfilled with the sealant emerging through the slots. The piston rings actvery much like the piston rings in motor car engines. When the ink isdispensed from the cartridge, the piston 30, due to its own gravity orweight and due to air pressure and the suction action caused by therotation of the ball 4, will move downwardly with the ink column so asto be constantly on top thereof. In doing so, the sealant in the gap 40will be distributed to fill substantially the entire space between thepiston and the wall of the tube 2.

Thus, contrary to prior art constructions wherein the entire or at leastthe major amount of the sealant is, from the very outset, lodged betweenthe piston and the tube, the present construction allows for storage ofthe bulk of the sealant protected from ink contact while the supply ofsealant between the piston and the tube is continuously replenished fromthis storage supply.

Moreover, if any ink moves to the annular space 40 surrounding thepiston member 30 and mingles with the sealing material, the uniqueconstruction of the piston in the present invention prevents permanentdegradation of the seal. This results from the fact that, as the pistonmoves forwardly in the cartridge leaving behind a deposit of material onthe cartridge wall, fresh and uncontaminated material from the supplywithin the cavity 34 is drawn through slots 24, 26 as described above toprovide a renewed seal. Furthermore, with substantially all of thesealing material effectively isolated from the ink and only a very smallquantity immediately adjacent thereto, the amount of sealing materialwhich could move into and mingle with the ink supply 12 in the cartridgeis effectively restricted to an absolute minimum as contrasted withconventional piston seals wherein substantially all of the sealingmaterial is in close proximity to the ink supply so that the ink canbecome contaminated with relatively large quantities of, sealingmaterial.

In the embodiment of the piston shown in FIG. 3, a cup-shaped pistonmember 130 having an internal cavity is provided with wall openings inthe form of peripheral slits 124- and 120 to provide communicationbetween the internal cavity and the external surface of the pistonwhereby sealant may be supplied from the internal cavity to the outsideof the piston. Thus, except for the absence of the peripheral grooves 20and 22 the structure and operation of a ball point pen utilizing thispiston member is the same as that described above with respect to thepiston member 3-0 of FIGS. 1 and 2.

In a typical ball point pen cartridge having an internal diameter of0.175 inch, the piston member of the type shown in FIGS. 1 and 2 had anoutside diameter of 0.170 inch, and an internal cavity of 0.134 inchdiameter, the depth of the internal cavity being 0.218 inch and thegrooves and slots in the walls having a width of 0.025 inch. Theperipheral grooves had a depth of from 0.006 to 0.018 inch. With thisarrangement, over 80 percent of the total initial quantity of sealingmaterial is contained within the cavity in the piston and therebypreserved from contamination so that fresh sealing material is availableeven when the piston approaches the forward end of the cartridge.

Although the invention has been described herein with reference tospecific embodiments, many modifications and variations therein willreadily occur to those skilled in the art. Accordingly, all suchvariations and modifications are included within the intended scope ofthe invention as defined by the following claims.

I claim:

1. A cartridge for a writing instrument comprising a tubular reservoircontaining writing fluid having a diameter larger than the diameternecessary to form a capillary for the writing fluid and having one endopen to the atmosphere, a narrow neck portion at the other end of thereservoir to supply writing fluid to a writing tip, a piston memberwithin the reservoir between the writing fluid and the open endcomprising a cup-shaped piston member having an outside diameterslightly smaller than the inside diameter of the reservoir, the pistonmember being formed with an internal cavity which is open to theatmosphere, a substantial reserve supply of temperaturestable sealingmaterial having a paste-like consistency within the cavity of thepiston, said piston member being provided with outwardly open,circumferentialiy extending slot means in communication with saidreserve supply of said sealing material in the cavity of the piston,said slot means extending circumferentially around the piston member forsupplying sealing material over the em tire inner wall of said tubularreservoir and comprising a plurality of circumferentially extendingslots positioned at diflerent levels lengthwise of the piston member,and an annular ring of the same sealing material which is substantiallysmaller in quantity than the reserve supply forming a seal between thepiston member and the wall of the reservoir and communicating with thesupply in the internal cavity through said slot means, whereby there isa substantially greater quantity in the piston cavity so that thereserve supply of sealing material in the cavity is isolated from thewriting fluid to preserve it from contamination thereby and as thepiston moves in the reservoir uncontaminated sealing material from thereserve supply passes through said slot means to replace the material inthe ring.

2. A cartridge according to claim 1, wherein said slot means extend forsubstantially 360 circumferentially around the piston member.

3. A cartridge according to claim 1, including groove means formed inthe outer surface of the piston member comprising at least one grooveextending circumferentially around the piston member and communicatingwith one of the slots of the slot means.

4. A cartridge according to claim 1, wherein the volume of the internalpiston cavity is equal to at least about percent of the total volume ofthe cavity and the space between the piston member and the wall of thereservoir.

References Cited in the file of this patent UNITED STATES PATENTS551,540 Fowler Dec. 17, 1895 2,777,422 Cofield et al Jan. 15, 1957FOREIGN PATENTS 1,028,325 France Feb. 25, 1953 1,097,511 France Feb. 16,1955

1. A CARTRIDGE FOR A WRITING INSTRUMENT COMPRISING A TUBULAR RESERVOIRCONTAINING WRITING FLUID HAVING A DIAMETER LARGER THAN THE DIAMETERNECESSARY TO FORM A CAPILLARY FOR THE WRITING FLUID AND HAVING ONE ENDOPEN TO THE ATMOSPHERE, A NARROW NECK PORTION AT THE OTHER END OF THERESERVOIR TO SUPPLY WRITING FLUID TO A WRITING TIP, A PISTON MEMBERWITHIN THE RESERVOIR BETWEEN THE WRITING FLUID AND THE OPEN ENDCOMPRISING A CUP-SHAPED PISTON MEMBER HAVING AN OUTSIDE DIAMETERSLIGHTLY SMALLER THAN THE INSIDE DIAMETER OF THE RESERVOIR, THE PISTONMEMBER BEING FORMED WITH AN INTERNAL CAVITY WHICH IS OPEN TO THEATMOSPHERE, A SUBSTANTIAL RESERVE SUPPLY OF TEMPERATURESTABLE SEALINGMATERIAL HAVING A PASTE-LIKE CONSISTENCY WITHIN THE CAVITY OF THEPISTON, SAID PISTON MEMBER BEING PROVIDED WITH OUTWARDLY OPEN,CIRCUMFERENTIALLY EXTENDING SLOT MEANS IN COMMUNICATION WITH SAIDRESERVE SUPPLY OF SAID SEALING MATERIAL IN THE CAVITY OF THE PISTON,SAID SLOT MEANS EXTENDING CIRCUMFERENTIALLY AROUND THE PISTON MEMBER FORSUPPLYING SEALING MATERIAL OVER THE ENTIRE INNER WALL OF SAID TUBULARRESERVOIR AND COMPRISING A PLURALITY OF CIRCUMFERENTIALLY EXTENDINGSLOTS POSITIONED AT DIFFERENT LEVELS LENGTHWISE OF THE PISTON MEMBER,AND AN ANNULAR RING OF THE SAME SEALING MATERIAL WHICH IS SUBSTANTIALLYSMALLER IN QUANTITY THAN THE RESERVE SUPPLY FORMING A SEAL BETWEEN THEPISTON MEMBER AND THE WALL OF THE RESERVOIR AND COMMUNICATING WITH THESUPPLY IN THE INTERNAL CAVITY THROUGH SAID SLOT MEANS, WHEREBY THERE ISA SUBSTANTIALLY GREATER QUANTITY IN THE PISTON CAVITY SO THAT THERESERVE SUPPLY OF SEALING MATERIAL IN THE CAVITY IS ISOLATED FROM THEWRITING FLUID TO PRESERVE IT FROM CONTAMINATION THEREBY AND AS THEPISTON MOVES IN THE RESERVOIR UNCONTAMINATED SEALING MATERIAL FROM THERESERVE SUPPLY PASSES THROUGH SAID SLOT MEANS TO REPLACE THE MATERIAL INTHE RING.